Protocol: RNAs were administered as described, with modifications [11]. A cocktail of siRNA simultaneously targeting TNF-α (Silencer® Select siRNA; s128522, Ambion, Austin, TX, USA), IL-6 (Silencer® Select siRNA; s217844, Ambion, Austin, TX, USA) and IL-1b (Silencer® Select siRNA; s127941, Ambion, Austin, TX, USA), as well as a control siRNA (Silencer® Negative Control #1 siRNA; Cat #4635, Ambion, Austin, TX, USA), were prepared immediately prior to administration by mixing the RNA (200 µM) with the transfection reagent, i-Fect™ (Neuromics, Minneapolis, MN, USA), in a ratio of 1 : 5 (w : v). At this ratio, the final RNA/lipid complex concentration was 2 µg in 5 µl for each cytokine siRNA and 6 µg in 15 µl for the control siRNA. The cytokine siRNAs were combined and they and the control siRNA (15 µl each) were delivered to the lumbar region of the spinal cord via the intrathecal catheters. Injections were given daily on 5 consecutive days (-1, 0, 1, 2, 3 d after L5 SNT.

The changes in mechanically induced allodynia and hyperalgesia in the rats surviving for 6 d after SNT are shown in figure. Allodynia and hyperalgesia were lower in the COCK group than in the CON group by 2 d after SNT (P < 0.05) and the difference was maintained for the duration of the experiment.

Figure: The time course of mechanical allodynia (A) and hyperalgesia (B) in the ipsilateral hind paw of rats undergoing L5 spinal nerve transection (SNT) after the administration of control siRNA (CON group) or a cocktail of small interfering RNAs (siRNA) targeting TNF-α, IL-6 and IL1-β (COCK group). The data on the rats surviving for 6 d after SNT are expressed as mean ± SE. -1: 1 d prior to SNT, 0: the day of L5 SNT, 1, 2, 4 and 6: 1, 2, 4 and 6 d after L5 SNT. *P < 0.05 vs. CON group at each time point. MPE: maximal possible effect. The cut-off values for mechanical allodynia and hyperalgesia are 30 g and 250 g, respectively.

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